InGaN与采用InGaN作为背势垒的双异质结的生长

我们研究了采用MOCVD生长了InGaN与InGaN和AlGaN/GaN/InGaN/GaN双异质结。我们发现InGaN的质量会严重影响AlGaN/GaN/InGaN/GaN双异质结的特性。通过优化生长压力与生长温度得到高结晶质量的InGaN薄膜。由于InGaN的极化方向与AlGaN的相反,使得GaN层与InGaN层之间出现了一个高势垒,提高了载流子的限域性并且降低了缓冲层的漏电。采用InGaN作为背势垒的双异质结的DIBL仅为1.5 mV/V。当VDS= 10 V时,测量得到的关态漏电流为2.6 µA/mm。     

具有InGaN背势垒且AlGaN层Al组分阶变的HEMTs结构的生长与表征

A novel In Ga N back barrier high electron mobility transistors structure with a compositionally stepgraded Al Ga N barrier layer was grown by metal organic chemical vapor deposition on sapphire substrate.The structural and electrical properties of two samples were investigated and compared:the first sample is the stepgraded structure and the second one is the high Al structure as a comparison.By calculating full width at half maximum of XRD measurements,the densities of screw-type threading dislocations are 8.34108cm2and11.44108cm2 for step-graded structure and high Al structure,respectively,which are consistent with the results of atomic force microscopy.By Hall measurements,the measured two-dimensional electron gas mobility was 1820 cm2/(V s) for step-graded structure,and 1300 cm2/(V s) for high Al structure,respectively.The stepgraded structure improves the crystal quality of Al Ga N layer due to the released lattice strain.The device was fabricated and leakage current is only 28 A when the drain voltage is 10 V; it was found that the In Ga N back barrier could effectively reduce the buffer leakage current.     

击穿电压提高的AlGaN/GaN/AlGaN双异质结特性

本文论述了AlGaN/GaN双异质结高电子迁移率晶体管的特性,该结构使用Al组分为7%的AlGaN来代替传统的GaN作为缓冲层。Al0.07Ga0.93N缓冲层增加了二维电子气沟道下方的背势垒高度,有效提高了载流子限阈性,从而造成缓冲层漏电的显著减小以及击穿电压的明显提高。对于栅尺寸为0.5100μm,栅漏间距为1μm的器件,AlGaN/GaN 双异质结器件的击穿电压（~100V）是常规单异质结器件的两倍（~50V）。本文中的双异质结器件在漏压为35V、频率为4GHz下,最大输出功率为7.78W/mm,最大功率附加效率为62.3%,线性增益为23dB。     

Preparation and properties of Ni/InGaN/GaN Schottky barrier photovoltaic cells

Ni/In_xGa_1−xN/GaN Schottky barrier solar cells with different In contents (x = 0.07/0.13) and two types of Schottky patterns (semitransparent current spreading layer and grid contact) are fabricated and the dependences of photovoltaic performances of these solar cells on In contents and Schottky patterns are studied. Solar cells with semitransparent contact have almost the same open-circuit voltages (V_oc) as solar cells with grid contact and exhibit a higher fill factor (FF). However, solar cells with grid contact exhibit a higher maximum output power density (P_max) than semitransparent contact due to their larger short-circuit current density (J_sc). On the other hand, V_oc and FF decrease significantly with increasing In content (beyond the decrease expected from the band gap of InGaN). By comparing the X-ray rocking curves, AFM images, dark current characteristics and spectral responsivities, it could be concluded that the deterioration of InGaN crystal quality with increasing In content is the dominant reason accounting for the strong decrease of V_oc and FF. In addition, using AMPS simulation, the band structure and ideal spectral responsivities are obtained. Comparison of the experimental and simulated results also shows that high crystal quality is a key factor to obtain high performance InGaN-based Schottky barrier photovoltaic cells.     

高质量立方相InGaN的生长

利用 LP- MOCVD技术在 Ga As( 0 0 1 )衬底上生长了高质量的立方相 In Ga N外延层 .研究了生长速率对 In Ga N质量的影响 ,提出一个简单模型解释了在改变 TEGa流量条件下出现的In组分的变化规律 ,实验结果与模型的一次项拟合结果较为吻合 ,由此推断 ,在现在的生长条件下 ,表面单个 Ga原子作为临界晶核吸附 Ga或 In原子实现生长的模型与实际情况较为接近 .对于晶体质量的变化也给予了说明 .得到的高质量立方相 In Ga N室温下有很强的发光峰 ,光致发光峰半高宽为 1 2 8me V左右 .     

InGaN/GaN超晶格垒层用于InGaN发光二极管发光增强研究

设计了InGaN/GaN超晶格垒层替代p-GaN和n-GaN附近传统GaN垒层的InGaN/GaN多量子阱(MQW)发光二极管(LEDs)结构。通过数值方法模拟出两种LED结构的光功率-电压(L-V)曲线、电致发光(EL)谱、能带图、电子浓度分布和辐射复合速率。结果表明InGaN/GaN超晶格替代n-GaN附近GaN垒层的LED结构比替代p-GaN附近GaN垒层的LED显示出更高的发光强度。这种发光增强的原因是InGaN/GaN超晶格替代n-GaN附近GaN垒层可以提高电子注入效率和辐射复合速率。     

InGaN背势垒AlGaN/GaN HEMT中的电流崩塌研究

Current collapses were studied,which were observed in AlGaN/GaN high electron mobility transistors(HEMTs) with and without InGaN back barrier(BB) as a result of short-term bias stress.More serious drain current collapses were observed in InGaN BB AlGaN/GaN HEMTs compared with the traditional HEMTs.The results indicate that the defects and surface states induced by the InGaN BB layer may enhance the current collapse.The surface states may be the primary mechanism of the origination of current collapse in AlGaN/GaN HEMTs for short-term direct current stress.     

Investigation of the current collapse induced in InGaN back barrier AIGaN/GaN high electron mobility transistors

Current collapses were studied, which were observed in A1GaN/GaN high electron mobility transistors （HEMTs） with and without InGaN back barrier （BB） as a result of short-term bias stress. More serious drain current collapses were observed in InGaN BB A1GaN/GaN HEMTs compared with the traditional HEMTs. The results indicate that the defects and surface states induced by the InGaN BB layer may enhance the current collapse. The surface states may be the primary mechanism of the origination of current collapse in A1GaN/GaN HEMTs for short-term direct current stress.     

表面应力诱导InGaN量子点的生长及其性质

为了得到高性能的 Ga N基发光器件 ,有源层采用 MOCVD技术和表面应力的不均匀性诱导方法生长了 In-Ga N量子点 ,并通过原子力显微镜 (AFM)、透射电子显微镜 (TEM)和光致发光 (PL )谱对其微观形貌和光学性质进行了观察和研究 .AFM和 TEM观察结果表明 :In Ga N/ Ga N为平均直径约 30 nm,高度约 2 5 nm的圆锥 ;In Ga N量子点主要集中在圆锥形的顶部 ,其密度达到 5 .6× 10 1 0 cm- 2 .室温下 ,In Ga N量子点材料 PL谱强度大大超出相同生长时间的 In Ga N薄膜材料 ,这说明 In Ga N量子点有望作为高性能有源层材料应用于 Ga N基发光器件 .     

单量子阱InGaN/GaN势垒高度与LED光电性能关系研究

通过对InxGa1-xN掺杂不同组份的In来改变InxGa1-xN的禁带宽度,从而改变量子阱势垒高度,并研究其与发光二极管光电性能、效率下降之间的关系。通过仿真模拟实验研究了不同量子阱势垒高度与InGaN /GaN量子阱发光二极管的功率光谱密度、内量子效率、发光功率及复合率之间的关系。分析结果表明：(1) In含量与发光二极管的光电性能并非成线性关系。(2) 在电流密度较低时,In组份越小,光谱密度峰值越大,发光功率越大。(3) 在电流密度较大时,In组份越大,光谱密度峰值越大,发光功率越大。(4) 光谱蓝移与电流密度大小紧密相关,电流密度大的蓝移程度大,反之越小。因此,应该根据不同的电流密度来选择In组份的大小,从而提高发光效率。     

Al在生长InGaN材料中的表面活化效应

为了解决材料的界面平整度,改善材料的晶体质量,在Ⅲ-Ⅴ族氮化物(InGaN)材料的生长过程中,加入了Al掺杂剂.实验发现,InGaN材料的双晶衍射半宽从533arcsec(非掺Al)下降到399 arcsec(轻掺Al),PL光谱半宽变窄,从21.4 nm(非掺Al)降为20.9 nm(轻掺Al).研究结果表明,Al作为活性剂明显提高了InGaN材料质量,这将对改善LED和LD多量子阱材料和器件质量带来积极影响,目前还没有相关的文献报道.     

Characteristics of AlGaN/GaN/AlGaN double heteroj unction HEMTs with an improved breakdown voltage

正We studied the performance of AlGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) with an AlGaN buffer layer,which leads to a higher potential barrier at the backside of the twodimensional electron gas channel and better carrier confinement.This,remarkably,reduces the drain leakage current and improves the device breakdown voltage.The breakdown voltage of AlGaN/GaN double heterojunction HEMTs (~ 100 V) was significantly improved compared to that of conventional AlGaN/GaN HEMTs(~50 V) for the device with gate dimensions of 0.5 x 100μm and a gate-drain distance of 1μm.The DH-HEMTs also demonstrated a maximum output power of 7.78 W/mm,a maximum power-added efficiency of 62.3%and a linear gain of 23 dB at the drain supply voltage of 35 V at 4 GHz.     

应用于大功率MMIC开关的AlGaN背势垒GaN HEMT

报道了应用于大功率开关的AlGaN背势垒0.25μm GaN HEMT。通过引入AlGaN背势垒,MOCVD淀积在3英寸SiC衬底上的AlGaN/GaN异质结材料缓冲层的击穿电压获得了大幅度的提升,相比于普通GaN缓冲层和掺Fe GaN缓冲层击穿电压提升幅度分别为4倍和2倍。采用具有AlGaN背势垒AlGaN/GaN 外延材料研制的GaN HEMT开关管在源漏间距为2μm、2.5μm、3μm、3.5μm和4μm时,估算得到的关态功率承受能力分别为25.0W、46.2W、64.0W、79.2W和88.4W。基于源漏间距为2.5μm的GaN HEMT开关管设计了DC-12GHz的单刀双掷MMIC开关。该开关采用了反射式串-并-并结构,整个带内插入损耗最大1.0dB、隔离度最小30dB,10GHz下连续波测试得到其功率承受能力达44.1dBm。     

MOCVD脉冲生长对InGaN太阳能电池材料的影响

通过对InGaN三元合金的生长方式做对比,发现在相同条件下,因常规生长过程中反应室In的浓度更高,生长出的InGaN中In组分更高。但是由于预反应的原因晶体质量较差,而脉冲生长由于源的分时输运,大幅减小了预反应的发生,提高了晶体质量。但由于生长时反应室In原子浓度变小,In的组分会降低,也会减小In滴的析出。     

LP－MOCVD生长InGaN单晶薄膜

报道了以Ａｌ２Ｏ３为衬底在ＧａＮ薄膜上ＬＰ－ＭＯＣＶＤ外延生长ＩｎＧａＮ单晶薄膜，并研究了ＩｎＧａＮ的生长特性。实验给出了ＩｎｘＧ１－ｘＮ合金的固相组分与汽相组分和生长温度的变化关系，并应用Ｘ射线衍射（ＸＲＤ）、Ｘ射线回摆曲线（ＸＲＣ）和室温光致荧光（ＰＬ）谱等技术对外延层的晶体质量、完整性和发光特性进行了分析。发现ＩｎＧａＮ／ＧａＮ系统中保持适当的压应力有助于提高外延层的晶体完整性，减少非故意掺杂杂质的引入，能改善外延层的发光特性。     

p型InGaN/GaN超晶格N面GaN基LED的光电特性

随着氮(N)面GaN材料生长技术的发展,基于N面GaN衬底的高亮度发光二极管(LED)的研究具有重要的科学意义.研究了具有高发光功率的N面GaN基蓝光LED的新型结构设计,通过在N面LED的电子阻挡层和多量子阱有源层之间插入p型InGaN/GaN超晶格来提高有源层中的载流子注入效率.为了对比N面GaN基LED优异的器件性能,同时设计了具有相同结构的Ga面LED.通过对两种LED结构的电致发光特性、有源层中能带图、电场和载流子浓度分布进行比较可以发现,N面LED在输出功率和载流子注入效率上比Ga面LED有明显的提升,从而表明N面GaN基LED具有潜在的应用前景.     

Microstructural Investigation of Bilayer Growth of In- and Ga-Rich InGaN Grown by Chemical Vapor Deposition

Epitaxial InGaN with an In content of up to 89% was grown on a GaN template on a sapphire substrate using metalorganic chemical vapor deposition. The grown layer showed a bilayered structure of In- and Ga-rich InGaN parallel to the growth plane, as confirmed by both x-ray diffraction and electron microscopy. High-angle annular dark-field images revealed that pyramidal Ga-rich InGaN had formed on the top of the In-rich InGaN layer with an abrupt interface. Nucleation of the In-rich InGaN was believed to be related to threading dislocations stemming from the GaN buffer layer.     

An extrinsic fmax > 100 GHz InAlN/GaN HEMT with AlGaN back barrier

We report the DC and RF performance of InAlN/GaN high-electron mobility transistors with AlGaN back barrier grown on SiC substrates. These presented results confirm the high performance that is reachable by InAlN-based technology. The InAlN/GaN HEMT sample showed a high 2DEG mobility of 1550 cm²/(V·s) at a 2DEG density of 1.7×10¹³ cm^-2. DC and RF measurements were performed on the unpassivated device with 0.2 μm "T" gate. The maximum drain current density at V_GS=2 V is close to 1.05 A/mm in a reproducible way. The reduction in gate leakage current helps to increase the frequency performance of AlGaN back barrier devices. The power gain cut-off frequency of a transistor with an AlGaN back barrier is 105 GHz, which is much higher than that of the device without an AlGaN back barrier at the same gate length. These results indicate InAlN/GaN HEMT is a promising candidate for millimeter-wave application.     

铟镓氮薄膜的光电特性

用金属有机物气相外延设备,在氮化镓/蓝宝石复合衬底上快速外延生长铟镓氮薄膜,并对其进行了X射线三晶衍射、光致发光、反射光谱及霍尔测量等实验测试.确定该薄膜为单晶,其中In组分可以从0增加到0.26;在光致激发下发光光谱为单峰,且峰值波长在360～555nm范围内可调;其发光机理被证实为膜内载流子经带隙跃迁而直接复合;并具有很高的电子浓度.但InGaN薄膜的结晶质量却随着In含量的增加而变差.